1. Field of the Invention
The present invention relates to a disk drive of a sector servo system for positioning and controlling a head at a target position on a disk, in accordance with servo information recorded in the disk, and, in particular, to a disk drive having a self-servo writing function of efficiently recording high density and high quality servo information in the disk.
2. Description of the Related Art
Conventionally, in a compact hard disk drive (HDD), servo areas (servo sectors) in which servo information is recorded are arranged at predetermined intervals on a disk. The servo information is read and reproduced by means of a head during data accessing. Based on this reproduced servo information the head is positioned and controlled at a target position (a target track). The servo information is usually written in a predetermined area on the disk by a device used exclusively for writing servo information (hereinafter called a servo writer) during the process of assembling the HDD.
FIG. 1A shows a state where the servo writer is set in the disk drive. The servo writer comprises a clamper (not shown in the drawing) fixing the casing 20 of the HDD, a fixed head 21 for reading/writing a reference signal, a driving plate 22 for positioning the head 2 of the HDD on an arbitrary position of the disk and a driving pin 24 for bringing the driving plate 22 into contact with a carriage arm 23. It further comprises a stepping motor 26 for driving the driving plate 22, a rack and pinion 27 for converting linear displacement generated by the stepping motor 26 into rotational displacement, an encoder 28 for detecting an amount of motion of the driving plate 22, a cable 30 for sending signals to and receiving signals from the disk drive to actuate the spindle motor 13, voice coil motor (VCM) 12 and head amplifier 29 of the HDD, a driving system control circuit, and a servo information recording/reproducing system control circuit (not shown in the drawing).
The HDD is fixed on the clamper (not shown in the drawing) so that the rotational centers of the driving plate 22, the rack and pinion 27 and the encoder 28 can be coincident with that of the carriage arm 23. The fixed head 21 for a reference signal is fixed to the outside of the HDD so as to be positioned at an arbitrary position other than a data area on a disk 1. This fixed head 21 detects a timing for writing servo information in accordance with the reference signal recorded in the disk 1. The reference signal is recorded typically in an area different from a track in which the servo information is written (a track used for normal recording/reproducing) in order to prevent overwriting produced by writing the servo information in the disk 1.
The driving pin 24, which contacts a portion of the carriage arm 23 allows the head 2 on an HDD main body to freely move to an arbitrary position on the disk 1, by rotating the driving plate 22. The driving pin 24 is brought into contact with a portion of the carriage arm 23. This portion of the arm 23 indicates the head placed oppositely to the disk 1, as shown in FIG. 1A, when a top cover 34 of the HDD is opened, or as shown in FIG. 1B when the driving pin 24 is inserted through a notched window 35 provided on a part of the top cover 34.
FIG. 1C is a fragmentary expanded view showing a positional relationship between the carriage arm 23 and the driving pin 24. To determine the position of contact between the driving pin 24 and the carriage arm 23, it is necessary to position the head 2 very accurately at an arbitrary position on the disk 1. For this reason, a contact position, where the amount of a positional shift from the tip of the head 2 is smallest, is on the carriage arm 23 which is more rigid than the head 2 and a suspension 25.
FIG. 1B shows an HDD using a servo writer of a conventional type. In this HDD, the driving pin 24 and the fixed head 21 are inserted respectively through the notched windows 35 and 36. The notched window 35 for the driving pin 24 is formed on the upper part of the top cover 34 and the notched window 36 for the fixed head 21 for a reference signal is formed on the side surface part thereof. In other words, to use the servo writer of a conventional type, it is necessary to form notched windows in predetermined positions on the casing portion of the HDD. These notched windows are kept open even during normal use of the HDD and thus may cause a deterioration in rigidity of the HDD casing or incursion of dust into it.
An explanation will now be given of the processing of servo information writing when the above-described conventional servo writer is used by referring to FIGS. 1A to 2.
First, a power is supplied to the servo writer, and a current is supplied via the cable 30 to the spindle motor 13, the head amplifier 29 and the VCM 12 of the HDD. Driven with the power supplied, the VCM 12 generates a force, moving the head 2 and the carriage 23 in the inner peripheral direction of the disk 1.
The fixed head 21 for reading/writing a reference signal writes only the number according to HDD specifications of reference signals SC generated from a reference signal generation circuit (not shown). Located away from the data area, the fixed head 21 is positioned at a predetermined position on the outer peripheral side of the disk 1. It not only adjusts the number of reference signals SC to be written, but also continues writing until a phase of each reference, signal SC and a phase of writing start/end of the reference signal SC coincide with each other within a predetermined allowable range.
The stepping motor 26 driven in accordance with a supplied power locates the head 2 and the carriage arm 23 on a track provided on the outermost periphery of the data area. In the meantime, as described above, the VCM 12 generates a force, moving the head 2 and the carriage arm 23 in the inner peripheral direction of the disk 1. Thus, by controlling the forces applied in opposing directions, in particular by controlling a force generated by the stepping motor 26, the head 2 can be positioned at a predetermined position on the disk 1. In this case, the encoder 28 monitors the position of the head 2. The head 2 writes signals from the outer periphery to the inner periphery of the disk 1. Alternatively, the head 2 may write signals in the reverse direction. In this case, however, forces must be generated so that the VCM moves the head 2 and the carriage arm 23 in the outer peripheral direction and the stepping motor 26 moves these in the inner peripheral direction. Also, contact positions between the carriage arm 23 and the driving pin 24 are caused to be opposite between the inner and outer peripheral sides of the disk 1.
When the positioning of the head 2 is completed, for instance as shown in FIG. 2, by means of the mechanism and the function described above, the reference signals SC read by the fixed head 21 are counted by an address counter 37, based on index signals (not shown in the drawing). The reference signals SC are then converted into address codes in a pattern memory 38 which stores the servo information beforehand in a host computer (not shown). Proper addresses on the pattern memory 38 are thereby selected. Servo information SD corresponding to the selected addresses is written in the disk 1 and a sector SS is formed. This processing is repeatedly performed for the tracks in which servo information is to be written and then writing of the servo information SD in the disk 1 is completed.
When this method for writing servo information is used, however, one servo writer is occupied just for completing writing of the servo information SD of one HDD. Therefore, a plurality of servo writers are required to simultaneously perform writing of bits of servo information SD of a plurality of HDDs, or one servo writer must write the servo information SD of all HDDs must be written one-by-one, spending a long time. This leads to a big reduction in HDD productivity. Furthermore, a very clean environment is needed in order to avert incursion of dust caused by opening the above-described notched window provided on a part of the HDD or the top cover.
Excitation generated by driving of the stepping motor 26 or the rack and pinion 27 imposes an influence on the positioning of the head 2 via a contact position between the driving pin 24 and the carriage arm 23. A rotational vibration component produced by rotating of the spindle motor 13 also affects positioning of the head 2. As a result, the head 2 may record a vibration component during the writing of the servo writer in the servo information SD. If the positioning of the head is controlled by using the servo information including such a vibration component, the positioning accuracy will naturally decline.
This is because the driving pin 24 for positioning the head 2 contacts only the carriage arm 23 and cannot directly control positioning of the head 2 for writing the servo information SC in the disk 1. This is also because rigidity of the servo writer cannot be increased in an unlimited manner or made completely uniform by eliminating variance, characteristics of HDDs and compatibility with the servo writer, so long as the HDD is fixed with the servo writer. These problems arise as long as the conventional method for writing the servo information in the disk 1 by using the servo writer is employed even when, for instance, high rigidity of a single servo writer or a single HDD casing is realized.
As described above, when the servo information is written by the servo writer, a great deterioration occurs in the quality of the servo information because of a vibration component produced by the servo writer, positioning accuracy of the head positioning control unit of the servo writer, a rotational vibration component produced by the rotation of the HDD spindle motor, a vibration component produced by shaking of the casing of the HDD main body by means of an exciting force of the rotation of the spindle motor, etc.
In recent years, efforts have been made to improve a track density in order to increase the capacity of a compact HDD. However, if a high track density is to realized, there will be greater effects on a track pitch from a vibration by the servo writer itself, the accuracy of the head-positioning control unit, an exciting force produced by an interaction between the head positioning control unit and an HDD main body and the like. These will then cause a decline in a quality of the servo information.
In an effort to solve these problems, consideration has been given to a development of a highly rigid servo writer producing fewer vibrations by providing a highly accurate positioning control mechanism. The manufacturing cost of such a mechanism and a servo writer, however, is very high. A servo writer must be developed for each kind of HDD machine, even an environment for performing writing of servo information must also be developed and, thus, productivity is low.